Rapid throttle plate maneuvers resulting in sudden engine acceleration or deceleration generate powertrain torque disturbances which may produce objectionable vehicle vibrational disturbances to occupants. The vibrational disturbances are comprised of transient, generally sinusoidal, longitudinal vibrations of the vehicle which gradually dampen out. These vibrational disturbances result in engine speed variations.
Prior art methods for minimizing the vibrational disturbances have comprised controlling the engine's ignition timing to produce a counteracting engine torque output. Such control methods have included (i) retarding the ignition timing by a predetermined value from its original setting at the moment of initial throttle plate movement, then restoring the timing to its original setting, or (ii) incrementally advancing and retarding the ignition timing in accordance with a derivative of engine speed.
The prior art methods of retarding the ignition timing by a predetermined value is directed to minimizing the largest vibrational disturbance which occurs at the time of initial acceleration. However, initiating ignition timing retard at the moment of initial throttle plate movement, prior to actual vehicle acceleration, rather than immediately preceding the vehicle acceleration often results in an initial ignition timing retard overcompensation characterized by significant torque loss, sluggish acceleration and possible misfire. Minimizing these undesirable characteristics requires limiting the amount of ignition timing retarded. Unfortunately, this also limits the degree to which vibrational disturbances can be counteracted.
The prior art methods of incrementally advancing and retarding ignition timing in accordance with a derivative of engine speed (.increment.RPM) is directed to minimizing the transient, sinusoidal, longitudinal vibrations by producing an appropriate engine torque output waveform for canceling the vibrations. However, the canceling waveform should be aligned 180.degree. out-of-phase with the waveform it is intended to cancel and not, as with the prior art, with the derivative of the waveform. As such, the prior art does not provide for an optimal canceling effect.